84 



MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



mancy after harvest (9). The percentage germi- 

 nation was low shortly after harvest and in- 

 creased to a peak after one year. Also in this 

 study it was shown that light conditions did not 

 affect percentage germination. Working on four 

 Astrebla species Jozwik and others (8) showed 

 that there was little germination below 22° C. or 

 above 38° C, and that, although a few seeds 

 germinated rapidly at 38° (within 13 hours), the 

 highest overall percentage germination was at 

 the lower end of the temperature range. These 

 germination tests were undertaken on older seeds 

 which had presumably passed any postharvest 

 dormancy. It is possible that the higher per- 

 centage germination at lower temperatures is a 

 general phenomenon of warm and hot rangeland 

 species. High-temperature inhibition of germi- 

 nation has a possible selective advantage in that 

 it prevents germination in the hot season when 

 there is a high evapotranspiration potential. 



Interest in the germination of range grasses 

 lies in the control mechanisms which have evolved 

 and the way these fit the plants to the adverse 

 environments. There is also a practical interest 

 in germination control as a means of propaga- 

 tion for experimental work on the control of 

 growth and development. A major problem in 

 any experimental work with natural popula- 

 tions, particularly of range species, is the problem 

 of low and erratic germination. From the stand- 

 point of influencing range management or pro- 

 moting plant welfare, germination is of little 

 significance. 



The period of establishment has, I believe, 

 been completely ignored in studies on Australian 

 rangeland perennial grasses. What characters do 

 these plants possess which enable the vulnerable 

 seedling to survive? Is root growth and pene- 

 tration exceptionally rapid? Is leaf growth de- 

 layed? Information of this type is available for 

 pasture grasses and, if available for range grasses, 

 would be a major contribution to our under- 

 standing of the physiological and morphological 

 basis of adaptation. 



Vegetative Growth 



In essence the grass seedling consists of an 

 abbreviated axis giving rise to leaves, alternately 

 on each side, as well as adventitious roots. As the 



seedling develops, the axillary buds grow into 

 tillers which, with their own adventitious root 

 system, may ultimately become independent of 

 the parent plant. Perennial herbage grasses 

 achieve their perenniality through the continued 

 production of tillers which in themselves may 

 be quite short lived ; they rarely survive more 

 than 18 months, although in some perennial range 

 grasses, tillers may survive for several years. 

 In that they are groups of annual or biennial 

 tillers, perennial grasses are morphologically and 

 physiologically different from other perennial 

 plants. 



The form of the perennial grass is determined 

 largely by the growth of the tillers. Those whose 

 tillers grow within the sheath of the subtending 

 leaf develop a tussock or bunchgrass form, while 

 those whose tillers grow out through the sheath 

 have a more lax form. In some grasses, under- 

 ground rhizomes are produced and vertical leafy 

 shoots grow from these .The life of a tiller ends 

 normally with the production of the terminal 

 inflorescence, although there is ample evidence to 

 show that this is not the fate of all tillers. Many 

 succumb to environmental or physiological condi- 

 tions which cause their earlier death. 



Herbage grasses and cereals have been used ex- 

 tensively in the study of both quantitative and 

 qualitative growth, and it is fortunate that we 

 have this information as a background for work 

 on rangeland species. Much is known about the. 

 nature of tiller and root growth, the effect of 

 the environment on morphogenesis including 

 flowering and dormancy, and the effect of grazing 

 and trampling on recovery and survival. In 

 Australia at least, it is time that this type of 

 investigation was extended to include the per- 

 ennial range grasses. 



A notable exception to the general lack of in- 

 formation on the growth of Australian range 

 grasses is the recent work of Jozwik (7), Jozwik 

 and others (8) Jozwik (unpublished), 4 and Joz- 

 wik and others (unpublished), 5 on the four spe- 

 cies of Astrebla: A. pectinata (Lindl.) F. Muell., 

 A. lappacea (Lindl.), A. elymoides Domin F. 

 Muell.. and A. squarrosa C. E. Hubbard. 



* F. X. Jozwik. Unpublished on Astrebla spp. 1970. 



5 F. X. Jozwik and A. 0. Xicholls. Growth and Develop- 

 ment of Astrebla pectinata (Lindl.) F. Muell. ex Benth. 

 under field conditions. Unpublished manuscript. 1971. 



